Something is just wrong with my SMR4 voicecard - SOLVED BY RESOLDERING

After I’ve spent all day reading through troubleshooting threads and doing some testing, comparing and resoldering I don’t know what to do anymore.
But from the start: I’ve assembled my Ambika with all voicecards and it plays fine. Now today I tried to tune the voicecards and on one voicecard I just get a click but no self oscillation even though when I play a synth voice and turn the cutoff it sounds ok. The problem I could narrow it down to is that IC’s 2, 3 and 4 have about half the voltage between pin 6 and 11 as on the working voicecards.
I’ve compared the voicecard with a working one and everything seems ok to my eyes (despite R3 is soldered reverse as on the other voicecards but since it’s not polarized that shouldn’t be the problem). I also resoldered some joints that looked flaky.
I also switched IC 5 and 4 with working voicecards.
Could need some hints what to check furthermore.

> about half the voltage between pin 6 and 11 as on the working voicecards.

This is a strange way of taking the measurement.

Measure between ground and pin 6 ; and between ground and pin 11. At least we’ll know which of the two rails is faulty…

I suspect a faulty connection on the stacking connectors - which would prevent the voicecard from receiving the negative rail.

thanks for the advice olivier!
Sorry, I just read it in some thread you recommended to someone to measure between pin 6 and 11.
when i measure between gnd and the pins i get no stable values? It keeps dropping all the time. I’ll resolder the connectors and see if that helps

resoldering the connectors didn’t help. I get 7,5v on pin 6 and and -3,5v on pin 11.

> I get 11,2v on pin 6 and and 3,5v on pin 11.

So now you get stable values?

It looks like the ground is floating… Is the ground pin of this voicecard continuous with a ground pin on another voicecard?

Maybe you could post a photo of your build…

no, still no stable values. I’ve just attached that particular voicecard right now and for measuring it was detached. should it be attached during measuring?

Can you explain how you made the measurement? I don’t get the bit about the voicecard being “detached”. How is the voicecard powered if it is detached?

sorry, my fault. it wasn’t powered…didn’t knew it has to be :[
so when i measure the attached, powered voicecard it measures stable 3,02v on pin 6 and -12,92v on pin 11 on IC’s 2, 3 and 4. I compared it to a working (attached) voicecardand the values are identical.

I don’t think you are doing it right… Where do you put the black lead of the meter and where do you put the red lead?

black lead to the 1st leg (left) of the right connector as i assumed it has to be jp4.
the red lead on the 6th leg (left side when you look onto it from above) and 11th leg (right side from above) on the ic’s.

The black lead must be on a grounded point.

like for example the ground on the jack connectors? Sry but i thought pin1 on jp4 is grounded. i just can’t read schematics

JP4 pin 1 is grounded indeed, but you are probably probing the wrong point. Your measurements look like you are probing a +5V point instead.

sorry for the confusion olivier. right, i did measure the other way round on the ic’s (counting from leg 16) but still reached the same legs. so now i get -7,93v on pin6 and 8v on pin11 (stable values, black lead on port 7 gnd). I double checked with a working vc and the values are identical. so the problem must be somewhere else…

problem solved :slight_smile: I systematically resoldered every single joint and obviously I had a flaky connection somewhere.